Hidden Danger: Venous Thromboembolism - RAD366-60

Hidden Danger: Venous Thromboembolism

by Connie Goldsmith, MPA, RN and Anna Ver Hage, MSN, AGACNP-BC, CCRN, CNRN
(4.5 / 794 ratings )

This course is credentialed for:
Radiologic Technology (1.00 CE Credit)

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A 52-year-old woman has been complaining of shortness of breath during the previous 24 hours. Upon clinical presentation, she has no swelling in her legs and no pain in her calves, and exhibits no signs of pneumonia. She denies any history of venous thromboembolism. She mentioned that she recently returned from a vacation in Hawaii, on which she was on a nine-hour flight. Her heart rate is 110 beats per minute with an oxygen saturation of 92% on room air. Could this patient have a pulmonary embolism (PE) and, if so, which diagnostic tests would you prepare this patient for?
Around 600,000 new or recurrent cases of venous thromboembolism, a term that includes deep vein thrombosis (DVT) and PE, occur in the United States annually.1,2 As many as 25% of patients with a PE die of a sudden death with no previous symptoms.1 Thirty-day survival rates for DVT are as high as 94.5% although if PE is present, with or without a DVT, the survival rate decreases to 55.6%.1 Venous thromboembolism causes between 100,000 and 180,000 deaths annually.2,3 It’s probable that more cases occur but remain undiagnosed.
In 2008, two major events helped draw attention to this potentially fatal condition: Medicare added venous thromboembolism after total knee and hip arthroplasty to its list of “never events,” stating this condition is an avoidable complication during hospitalization. Its occurrence could result in decreased reimbursement to the facility.4 And the U.S. Department of Health and Human Services published The Surgeon General’s Call to Action to Prevent Deep Vein Thrombosis and Pulmonary Embolism.2
Killer Legs
A thrombus is a blood clot that fully or partially obstructs a blood vessel. An embolus is a particle of material that circulates within blood vessels. It may be a portion of a broken thrombus, plaque, an air bubble or a piece of foreign matter. Most venous thrombi originate within the deep veins of the calves and thighs.1
© 2008 A.D.A.M., Inc.
Blood clotting is a complex mechanism, and when the body fails to normally dissolve a clot, it can enlarge. As the size of the thrombus increases, it fully or partially impedes return of venous blood to the heart. As the lumen of the vein narrows, blood and fluid accumulate distal to the thrombus. A dangerous and potentially deadly PE occurs when pieces of the thrombus break off and travel through the circulation to lodge in the pulmonary vasculature.
Three elements, named Virchow’s triad, trigger venous thrombosis. These elements are venous stasis, primary or acquired hypercoagulability and vessel wall injury.2,5,6
Venous stasis: Decreased or sluggish blood flow is a major cause of DVT. This decrease in blood flow usually occurs during periods of extended immobility, such as after acute illness, during recovery from major surgery, after trauma, during pregnancy and in the postpartum period.2,5,6
A well-known risk factor for DVT is the prolonged time spent sitting during a long plane flight. With more than 2 billion people boarding commercial airlines annually, this problem has earned the nickname “economy-class syndrome,” reflecting the cramped spaces and immobility common to such flights.7 Travel by air (car, train, etc.) for four or more hours increases the risk for DVT twofold for several weeks after the trip.2 People on flights of eight hours or more experience up to a fourfold increase.7 Immobilization is the cause of about 75% of travel-related DVT, occurring more often among people who sit in window or middle seats.7
A five-year cohort study of 8,755 frequently traveling employees of international organizations confirmed the two- to fourfold increase in risk for venous thromboembolism, especially among people younger than 30, women on oral contraceptives and the unusually tall, short or overweight.8 (Level B) The risk increased with the frequency and duration of flights.8 (Level B)
Hypercoagulability: A number of inherited hypercoagulable states known as thrombophilias (i.e., deficiency of the naturally occurring anticoagulant antithrombin, among others) contributes to a state of abnormal coagulation.2,9 Factor V Leiden, a genetic clotting disorder, is present in about 15% to 20% of patients with venous thromboembolism.2 One large case-control study concluded travelers with factor V Leiden have an eightfold increase in the risk for venous thromboembolism.9 (Level B) Hypercoagulability also occurs with dehydration, sickle cell disease and some cancers (especially among people receiving chemotherapy), as well as during pregnancy.2,6,9 Oral contraceptives and hormone replacement therapy, including raloxifene (Evista) for osteoporosis, are also believed to increase hypercoagulability.2,6,9
Vessel wall injury: Injuries to vessel walls draw platelets and inflammatory mediators to the area. These substances stimulate clotting and may activate the coagulation cascade. Conditions that damage vessel walls include mechanical trauma, indwelling IV catheters, history of DVT, hypertension, infection and chronic inflammation of vessels from smoking.2,6 (Assess your risk factors for DVT on the Coalition to Prevent Deep-Vein Thrombosis Web site.)
Lowering the Risk for Travelers
DVT is largely preventable. In healthy people without a history of DVT, lifestyle modifications, such as maintaining a normal weight and exercising regularly, benefit the circulation. People with a body mass index higher than 30 have a two- to threefold increase in risk for DVT, with a greater risk for those with a BMI higher than 40.2 Maintaining adequate hydration and limiting alcohol intake may be beneficial. Avoiding smoking, controlling blood glucose and managing hypertension can also help as these factors are blood vessel irritants. Diet modifications have also proven beneficial in reducing risk. In a 12-year longitudinal study of about 15,000 adults, those who ate more fish, fruit and vegetables, had a lowered incidence of venous thromboembolism, while those who ate the highest percentage of red and processed meat had a greater risk; eating fish even once a week lowered the risk of venous thromboembolism by 30% to 45%.10 (Level B)
Actions to reduce immobility during travel can be lifesaving. It is important to educate your patients on measures to reduce the risk for travel-related venous thromboembolism. These measures include:
  • Walk briskly around the airport for half an hour before boarding the plane
  • Avoid dehydration; drink 8 ounces of water every hour or two
  • Avoid alcohol, caffeine and salty foods that contribute to dehydration
  • Walk up and down the aisle once an hour
  • Don’t cross legs or knees
  • Exercise the lower extremities a few minutes each hour while seated
  • Wear graduated compression stockings to reduce the risk for DVT. (In one systematic review only 0.16% of air passengers who wore compression stockings developed DVT while 3.6% who wore no stockings developed DVT.7)
People at moderate to high risk for DVT who do not take anticoagulants should discuss with their physician whether to take a prophylactic dose of an anticoagulant, such as low-molecular-weight heparin, before travel.7
Managing the Risk for Medical and Surgical Patients
Most hospitalized patients are at high risk for venous thromboembolism, whether they are medical patients (cancer, heart attack or stroke); surgical patients (especially orthopedic, gynecologic or urologic surgery); or maternity patients. Ten percent to 40% of medical and general surgery patients develop venous thromboembolism while 40% to 60% of major orthopedic surgery patients develop venous thromboembolism. Therefore, every patient must be assessed for prophylaxis.2
Preventive measures for DVT include both mechanical and pharmacological interventions. Mechanical measures in hospitalized or bedridden patients include graduated compression stockings and sequential compression devices, which include intermittent pneumatic compression devices and venous foot pumps. Sequential compression devices help to reduce venous stasis, improve blood flow and increase the level of circulating fibrinolysins.5 They are safe, well tolerated and, among low-risk patients, may decrease the incidence of DVT by 60%.5 Sequential compression devices are especially valuable for surgical patients for whom pharmacological therapy may be risky.11 In one study, however, adherence to prescribed use of the devices varied from 48% on medical/surgical floors to 78% in ICUs.11 (Level B)
Another option for mechanical preventive therapy is the use of permanent or retrievable implantable filters in the vena cava. These devices look like tiny umbrellas with microscopic holes that allow for trapping of blood clots to prevent PE without impeding blood flow.2 Most hospitalized patients at high risk for venous thromboembolism, however, should be on preventive anticoagulant therapy unless contraindicated.2
A number of professional medical organizations have developed evidence-based guidelines for the prevention and treatment of venous thromboembolism. While all the guidelines recommend the use of pharmacological prophylaxis for patients at risk for venous thromboembolism, some hospitals and physicians do not adhere. One epidemiological study of nearly 5,550 patients at 183 hospitals with confirmed DVT found that the majority had not received recommended preventive anticoagulant therapy despite their high risk.2 Orthopedic surgery patients are more likely to receive preventive anticoagulants — up to 93.7% in one study —than other surgical patients.2
The American College of Chest Physicians (ACCP) recommends prophylactic anticoagulant therapy for moderate to high-risk patients during surgery, including major gynecologic surgery, open urologic procedures, bariatric surgery, thoracic and cardiac surgery, elective hip and knee replacement, and repair of hip fracture, as well as for major trauma patients.12 (Level ML) The ACCP also recommends anticoagulants for certain acutely ill medical patients, such as those with congestive heart failure, severe respiratory disease and cancer.12
Recommended medications for venous thromboembolism prevention include low-dose unfractionated heparin, low-molecular-weight heparin, fondaparinux or vitamin K antagonist. The guidelines also specify the target International Normalized Ratio (INR), the measurement of the degree of anticoagulation.12 The ACCP guidelines outline detailed dosing instructions.12 (Level ML)
Origin and Diagnosis of DVT
Eighty percent of DVT originates in the venous sinuses of the calf muscles although it can arise in the femoral or iliac veins and, although rare, in major veins of the upper body.13-15 About 20% of calf DVT extends upward into the proximal popliteal, iliac or femoral veins, at which point it may break off and travel to the lungs.15
DVT that involves only the calf veins is less often associated with an increased risk of PE but is associated with development of post-thrombotic syndrome (chronic venous insufficiency). About half the people who develop DVT are asymptomatic; their bodies may dissolve the thrombus or develop collateral circulation to bypass the occluded site.14,15 When symptoms are present, they occur in only one leg and may be misleading; these atypical symptoms may be pain in the ball of the foot when walking, fatigue in the leg or fever. More definitive symptoms, such as reddish-blue discoloration and pain and warmth in the leg or calf, strongly suggest DVT. The affected leg may be noticeably larger. The patient may complain of painful muscle cramps in the calf or pain behind the knee that intensify for a time. When the pain worsens, it may be relieved by elevation. Homans’ sign, pain in the calf upon dorsiflexion of the foot while the leg is extended, has long been considered a classic sign of DVT although its absence does not rule it out.6
The American Academy of Family Physicians and the American College of Physicians jointly developed evidence-based guidelines for the diagnosis of venous thromboembolism.16 Recommendations 1 to 3 below relate to DVT.16
Recommendation 1: Validated clinical prediction rules, such as the Wells Criteria for DVT, should be used to estimate pretest probability of venous thromboembolism.16 The Wells tool assigns a point value to clinical findings and stratify patients into low-, intermediate- and high-risk groups:16
  • Cancer (during treatment or treatment within the past six months): 1
  • Paralysis, paresis or recent immobilization of lower extremities: 1
  • Recently bedridden more than three days or major surgery within 12 weeks: 1
  • Tenderness along distribution of deep venous system: 1
  • Entire leg swollen: 1
  • One calf swollen 3 cm more than the other calf: 1
  • Pitting edema only of affected leg: 1
  • Presence of superficial veins: 1.
  • Alternative diagnosis at least as likely as DVT: -2
Risk of DVT: low = 0; intermediate = 1-2; high = 3 or more
Recommendation 2: Patients with low pretest possibility of DVT should have a D-dimer test (a blood test that measures thrombin and plasmin activity), which has a 96% to 100% negative predictive value; patients with negative D-dimer tests are unlikely to have DVT.16
Recommendation 3: Duplex ultrasound is recommended for patients with intermediate to high probability of DVT. Contrast venography, the definitive test to rule out the diagnosis of DVT, may be indicated for certain patients. In this procedure, a catheter is threaded into the vein, and dye is injected. Images are taken to determine venous patency.16
The initial goals for DVT treatment are to prevent the clot from growing, embolization and recurrence, as well as to limit the development of post-thrombotic syndrome.14,15 Treatment generally consists of anticoagulation with either a standard or weight-based dosing of unfractionated heparin (usually by IV continuous infusion after a loading dose), low-molecular-weight heparin subcutaneously or fondaparinux.13-15 Treatment should include appropriate measurement of activated partial thromboplastin time and INR, depending on the anticoagulant prescribed.14,15 Warfarin may be started immediately, and patients are likely to be discharged on anticoagulants (low-molecular-weight heparin or fondaparinux) in addition to the warfarin.13-15 These anticoagulants should be continued for a minimum of five days, and when the INR is less than 2 for two consecutive days, the low-molecular-weight heparin or fondaparinux can be discontinued.13 (Level ML) The goal INR for patients on long-term anticoagulation is between 2 and 3.13
Pharmacomechanical catheter-directed thrombolysis (PCDT) is another treatment option that allows for removal of the thrombus. An interventional radiologist inserts a catheter directly into the venous clot and dissolves it with a fibrinolytic drug and, therefore, promptly restores blood flow. This is not considered a first-line treatment and is usually reserved for patients who have not responded to anticoagulation.17 (Level A) There has been discussion about the benefits of using this therapy and its role in reducing the risk of post-thrombotic syndrome. The Acute Venous Thrombosis: Thrombus Removal with Adjunctive Catheter-Directed Thrombolysis Randomized Control Trial is under way to assess if PCDT as an adjunct to standard DVT treatment does have a role in decreasing the risk of post-thrombotic syndrome.17 (Level A)

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